Oscillator



OLJHMM HUJL H. H. GRIMM OSCILLATOR arch 18, 1952 3 Sheets-Sheet 1 FiledDec. 29, 1944 INVEN TOR. #[MV 6. aim/)7 BY W mam- H. H. GRIMM March 18,1952 OSCILLATOR 3 Sheets-Sheet 2 Filed Dec. 29, 1944 March 18, 1952 H.H. GRIMM 2,589,246

OSCILLATOR Filed Dec. 29, 1944 :s Sheets-Sheet s Patented Mar. 18, 1952OSCILLATOR Henry H. Grimm, Dayton, Ohio, assignor to the United Statesof America as represented by the Secretary of War Application December29, 1944, Serial No. 570,421

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 3 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

The invention to be hereinafter described relates to wide range cavityoscillators.

In oscillators of this general type one serious objection anddisadvantage has been a high noise level during tunin of the oscillatordue, primarily, to engagement of the sliding contacts. In knownoscillators of this type it has been common practice to use what isknown as the double concentric cavity construction involving aconsiderable number of parts with total considerable length andcorresponding complexity of adjustments. In the known oscillators ofthis general class there are serious restrictions controlling thetracking of the feed-back capacity with I and I0.

the main capacity, as the feed-back capacity needs to be increased asthe resonant frequency decreases to insure that the oscillator outputdoes not cease at low frequencies.

The main objects of the present invention are to overcome the above andother objections and disadvantages and provide a simple, efiicient,compact, wide range cavity oscillator of few parts and capable ofrelatively low cost production.

In order to more clearly disclose the construction, operation and use ofthe invention, reference should be had to the accompanying drawingsforming part of the present application.

Throughout the several figures of the drawings like reference charactersdesignate the same parts in the different views.

In the drawings:

Fig. 1 is a longitudinal cross section through a preferred form of theinvention;

Fig. 2 is a like view through a modified form;

Fig. 3 is a circuit diagram through the invention, in the modification;and

Fig. 4 is a like diagrammatic view showing the circuit through thepreferred form.

Referring to the drawings in detail, I indicates the wall or barrel ofthe oscillator in which the cavity exists. The opposite ends are closedby heads 2 and 3. Beyond the head 2 and suitably supported thereon is acylindrical section, frame or other suitable support or guide 4. Frame 4carries a block or head 5 in which is removably mounted the bearingblock or head 6, of rod I5.

From the base 3 a stub I extends longitudinally toward head 2concentrically within the cylinder I. The upper portion of this stub istapered or conical, the top being cut off on a plane parallel with thebase, producing a frustum 8. Coopcrating with frustum 8 is the movablecup 9. Cup 9 comprises a head mounted to travel longitudinally back andforth within I. Cup 9 is of very slightly less outside diameter than theinside diameter of I. It is provided with a skirt or wall I0perpendicular to its base. In assembled, operative position, this skirtwill be, as shown, concentric with but very slightly spaced from theadjacent wall of I. There will be no actual physical contact between thesurfaces of This reduces to the minimum the noise during tuning of theoscillator.

Concentric with skirt I0 is a cylindrical block in which is provided asocket or well II the lower inner portion of which has dimensionssubstantially the same as corresponding dimensions of the frustum 8. Theadjacent and cooperating surfaces of 8 and II are substantiallycomplementary.

In order to travel the cup 9 longitudinally within the cylinder I towardand from the stub I, a stem, post or tube I2 is connected theretoconcentrically thereof. This tube has sliding longitudinal movementcentrally in and through the head 2, but is held against rotary movementtherein by a spring pressed detent or any other suitable device I3working in a longitudinal groove HI in I2, in well known manner. Forreciprocation of tube I2, the upper portion thereof is interiorly screwthreaded to receive the cooperating threaded rod I5. This rod is notthreaded through the bearing block or head 6 but, instead, is integraltherewith and both the rod and the bearing block rotate as a unitrelative to head 5. Shaft I5 and bearing block or head 6 are heldyieldingly in place by leaf springs 25 or the like. By rotating rod I5by a knob or any other suitable means not shown, the lateral distance orair-gap between II and 8 may be varied as may be desired. Also, and atthe same time, the effective lengths of the overlapping walls orsurfaces of 8 and II may be correspondingly varied, all for purposeswell understood in the art. By adjustment of the tapered surface I Irelatively to the tapered surface 8 the lateral distance between the twomay be reduced to two or even one thousandth of an inch which makes itpossible to control or regulate the capacity over a wide range and witha fine degree. However, mechanical difiiculties in manufacture makeefforts at this extreme adjustment inadvisable. The tolerancesnecessarily permissible in manufacture result in irregularities which,at such extreme adjustment, result in actual contact or pacitor.

such near contact, relative to other portions of the cooperatingsurfaces 8 and II, as will render inoperative the capacitor 8-| I.However, within the practicable range of adjustment, the capacitor 8-||is capable of giving much finer control and better results than otherconstructions for the same general purpose.

As will be readily understood, the cylinder I and. skirt ID, in spacedrelation, provide a construction and arrangement capable of acting as acondenser of fixed capacity which may serve or function as a radiofrequency by-pass.

To complete the assembly as an oscillator, a triode tube, indicated as awhole by IT, is suitably mounted in the cavity between 9 and 3. Thistube may be one of several known types such as that generally referredto as the lighthouse type tube or that known as the acorn type. Asillustrating the invention, the lighthouse type has been selected and isindicated, generally, at H. Should the acorn type be substituted for thelighthouse, those skilled in the art will readily understand that thetube capacities themselves supply sufficient feedback, requiring no suchfeed-back arrangement as that advisable with the lighthouse type. Thetube plate is connected to the power supply (B+) and to a by-passcondenser. The other side of the by-pass condenser is connected to thestub 1 and through it to the variable capacitor.

In the preferred construction, a lighthouse tube I! being used, avariable feed-back condenser is included, comprising a smallcapacitative tab |8 fixed at its outer end to the framework supportingthe tube. It is resilient. Its inner free end is yieldingly adjustabletoward a plate l9 which is mounted on stub I. A threaded and insulatedrod or a rod 20 of insulating material extends through head 3 andengages the under side of I8. Thus the free end of l8 may be yieldinglyforced toward l9 but will return to its originally greater spacedrelation therefrom as soon as the force on 20 is removed. As will bewell understood, 8 and I9 constitute an external variable feed-backcondenser for tube l1. With the variable capacitor 8-| I in a givenrelation or position, the plate 18 may be manually adjusted to properlyeffect the desired corresponding feed-back. Thus, the feed-back isvariable and adjustable. However, it must be changed for the respectivechanged relation between 8 and In Fig. 2, a modification is illustratedincluding a variable feed-back condenser, automatically operated, thevariation in the feed-back corresponding with the variation in thevariable ca- In this form, plate |9 is omitted and a filament lead issubstituted for rod 20. The variable feed-back condenser in thismodification operates automatically and in such manner that itsoperation changes in accordance with the variation of the variablecapacitor 8-| I. It consists of two stationary spaced plates 2| and 22and the movable plate 23. Plate 2| is carried by a rod, bar, strip orother suitable support passed through the wall of and connected to anceto the travel of 9. It is so positioned as to extend between plates 2|and 23. As it is moved back and forth between 2| and 22 by travel of 9it will have the same condenser effect or action as obtained by movementof tab l8 relatively to plate IS in the preferred form. However, a veryimportant feature of difference between the two types of variablefeed-backs results from the fact that plate 23 producing the variationin the modification is, carried by and travels with cup 9 of thevariable capacitor 8| As a result of that relation, the variation in thefeed-back will, approximately, correspond with the variations in thevariable condenser 8-, thereby giving a wider frequency range withoutfeed-back adjustment.

As will be clear from the drawings of the modified form, particularly asindicated in the diagram, all leads to the oscillator are brought in atthe shorted end of the stub which makes up the inductance of theresonating circuit.

Referring particularly to Fig. 3 the oscillator, briefly, is what isknown as a grounded grid untuned cathode oscillator circuit. It may betraced in the diagram of Fig. 3 substantially as follows: The tunedcircuit inductance consists of stub I, head 3 and the wall The variablecapacitor consists of adjacent surfaces 8| The radio frequency by-passcondenser consists of skirt HI and wall I. The blocking and radiofrequency by-pass condenser |0|l isolates the plate voltage from themetal structure of the cavity. The grid condenser |0| is built in theside of the cavity. Chokes I02 and I03 are required in the cathode andfilament leads of the grounded grid oscillator, as will be wellunderstood. The variable feed-back capacity is shown at 2|22. The tubeused in this diagram is a lighthouse triode.

Fig. 4 is a schematic diagram of the preferred embodiment illustrated inFig. 1. Fig. 4 is essentially the same as Fig. 3 except that instead ofthe feedback capacitor 2|-22 of Fig. 3, there is shown the feedbackcapacitor |8--|9 which is not automatically operated, but is manuallyoperated to perform the same function as capacitor 2|22. In all otherrespects both circuits operate in the same manner.

It is thought that the construction, operation and use of the inventionwill be clear from the preceding detailed description.

Changes may be made in the construction, arrangement and disposition ofthe several parts of the invention, within the scope of the appendedclaims without departing from the field of the invention and it is meantto include all such within this application wherein only a preferredform and one modification have been disclosed by way of illustration andwith no thought or intent to, in any degree, limit the inventionthereby. i

Having thus described my invention, what I i claim and desire to protectby Letters Patent is: 1. A cavity oscillator including a cylindrical 65,b dy, a first member connected to and forming a closure at one end ofsaid cylindrical body, said first member being provided with astationary stub extending within said cylindrical body concentricallytherewith, said stub having a conical surface on the end thereof,connecting means disposed within and insulated from said stub, saidconnecting means cooperating with said stub to form a coupling condenserhaving a low reactance to the radio frequency energy generated by saidoscillator, an electron tube having QLHHLJH MUUL a cathode, an anode anda control electrode, means insulated from said stub for connecting saidanode to said connecting means, means for connecting a source ofspace-current voltage between said connecting means and said firstmember, a first condenser element connected to said control electrodeand arranged in spaced relationship with respect to said cylindricalbody, a second condenser element connected to said anode, a thirdcondenser element connected to said cathode and arranged in spacedrelationship with respect to said second element, a second memberlongitudinally movable within said body relative to said stub andprovided with a fourth condenser element cooperating with the conicalsurface of said stub, said second member also carrying a cylindricalflange in spaced relationship to said cylindrical body to form a fixedcondenser, and means for moving said movable 3. A cavity oscillatoraccording to claim 1, wherein said tube is disposed with the top thereofwithin said cylindrical body and adjacent to said stub, the axis of saidtube being substantially perpendicular to the axis of said cylindricalbody, said tube having an anode terminal on the top thereof, and whereinsaid means for connecting said anode to said connecting means includes acap connected to said anode, said cap including a stud passing throughand insulated from said stub and contacting said connecting means.

HENRY H. GRIMM.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,223,835 Smith Dec. 3, 19402,248,227 Gantet July 8, 1941 2,328,561 Lavoie Sept. 7, 1943 2,408,355Turner Sept. 24, 1946 2,435,442 Gurewitsch Feb. 3, 1948 ,438,832 TurnerMar. 30, 1948 2,443,907 Gurewitsch June 22, 1948 2,458,650 SchreinerJan. 11, 1949

